Interpretive Summary: Dietary components and changes cause shifts in the ruminal microbial ecology that can play a role in animal health and productivity, but the magnitude of these changes remains unknown. The objective of this study was to utilize pyrosequencing to analyze the diversity of ruminal bacterial populations of cattle fed citrus pulp pellets (CPP), which are fed to cattle to improve animal growth and have an impact on foodborne pathogenic bacteria in live cattle. 0, 10, or 20% of the concentrate portion of the ration was replaced with citrus pulp pellets (CPP,) and the microbial population of the rumen was found to change only slightly. Overall, there were relatively few changes in ruminal microbial populations possibly due to a lack of essential oils in the CPP which are thought to be critical in the alteration of ruminal microbial populations.

Technical Abstract:
The rumen microbial ecosystem remains a mystery from a quantitative perspective. Dietary components and changes cause shifts in the ruminal microbial ecology that can play a role in animal health and productivity, but the magnitude of these changes remains unknown. The objective of this study was to utilize pyrosequencing to analyze the diversity of ruminal bacterial populations of cattle fed citrus pulp pellets (CPP). Heifers (n=180; 218.3±2.4 kg) were fed a basal feedlot diet and randomly assigned to one of three diets (n = 60/diet). In each diet, 0, 10, or 20% of the concentrate portion of the ration was replaced with citrus pulp pellets (CPP). Using bTEFAP, the ruminal microbiota of cattle were examined using modern molecular methods to understand how different levels of a common by-product feedstuff affect ruminal microbial ecology. Prevotella and Eubacterium were found to be the predominant bacterial genera in the rumen, comprising 34% and 6%, respectively, of the bacterial population. The Firmicutes:Bacteroidetes (F:B) ratio showed an increasing trend (P = 0.07) in animals fed CPP when compared to controls. Butyrivibrio and Carnobacterium proportions increased with increasing amounts of CPP in the diet, while in contrast, the proportions of Dialister and Catonella declined. An increase in the proportion of Bacillus was observed concurrently with increases in dietary CPP. Overall, there were relatively few changes in ruminal microbial populations, possibly due to a lack of essential oils in the CPP which are thought to be critical in the alteration of ruminal microbial populations.